Air modulated siren having concentric cylinders



July 1, 1969 F. M. MURRAY 3,453,616

AIR MODULATED SIREN HAVING CONCENTRIC CYLINDERS Filed D96. 23, 1966 Sheet I G1 3 lo s08 /I ////"1 a 1 2 )8 3 I 72 5 am s 2 21c; m; .r F g BUB 227/ v fiv 1 .3\\\\\\\\\\\\\ 4g 40 A; Z A: l A 24 1 {L ie S //VVE/V7TOP FA Name/e A4. MURRAY A FOAM/5Y5 F: M. MURRAY 3,453,616

AiR MODULATED SIREN HAVING CONCENTRIC CYLINDERS July 1, 1969 Sheet of 3 F 'iled Dec. 25, 1966 N V N T0 FA MCI/E 44. Mule 8 A FOR/V5 Y5 July 1, 1969 v MURRAY 3,453,616

AIR MODULATED SIREN HAVING CONCENTRIC CYLINDERS Filed Dec. 23, 1966 Sheet 3 of 3 LOAD United States Patent 3,453,616 AIR MODULATED SIREN HAVING CONCENTRIC CYLINDERS Fancher M. Murray, Huntsville, Ala., assignor to Wyle Laboratories, Huntsville, Ala., a corporation of California Filed Dec. 23, 1966, Ser. No. 604,225 Int. Cl. Gk 7/06 US. Cl. 340-404 10 Claims ABSTRACT OF THE DISCLOSURE An air modulated loud speaker construction employing a pair of slotted concentric cylinders in the modulator assembly. The concentric cylinders respectively comprise an armature and a stator which are coupled together by a cylindrical spring which permits axial movement of the armature relative to the stator. By permanently coupling the armature and stator in this manner, the modulator assembly can initially be precisely assembled so as to prevent any future misalignment between the armature and stator.

This invention relates generally to acoustic apparatus and more particularly to an improved air modulated loudspeaker construction.

Many diflerent air modulated loudspeaker constructions are discussed in a Stanford Research Institute report of Dec. 30, 1955, entitled Development of a Modulated Air Stream Loudspeaker, by J. C. Burgess and V. Salmon. Essentially, all of these loudspeakers constructions are comprised of a pneumatic valve whose impedance is varied in response to an electrical input signal. Variations of the input signal cause corresponding fluctuations in an air flow which is supplied to the loudspeaker by an air com pressor. These fluctuations, superimposed upon the direct air flow, constitute the radiated sound. By this means, a small amount of electrical energy can control a large amount of acoustic output.

Although air modulated loudspeakers may be used to reproduce intelligible speech, they are more often used where a controlled extremely high energy acoustic output is desired. Thus, they may find utility as foghorns, for example. In addition, they find significant utility for environmental testing purposes where it may be desired to simulate very loud noise levels as might be produced by jet engines. Regardless of the application, it is always desirable that the loudspeaker be efficient and reliable, and easy to assemble, maintain, and adjust.

Many prior art loudspeaker constructions employ a pair of slotted concentric cylinders as the pneumatic value or modulator assembly. In such constructions, a first of the cylinders, the stator, is securely anchored to some heavy structure and a second of the cylinders, the armature, is mounted for axial movement relative thereto. Normally, the armature is secured to the heavy structure through some type of soft suspension. Freqeuntly, the soft suspension consists of radial springs, e.g. of rubber, which are attached to the armature by epoxy bonding. Means, for example a voice coil carried by the armature, and acting in a permanent magnetic field, are provided for exerting a force on the armature to move it in an axial direction relative to the stator. As a consequence, the degree of alignment between slots defined in the armature and slots defined in the stator can be varied to thus vary the impedance to the air flow.

In order for the loudspeaker to operate with maximum eificiency, the alignment of the slots in the armature with respect to those in the stator becomes very critical. Misalignment by as little as .001 inch can appreciably reduce ice the output power available from the loudspeaker. Inasmuch as such loudspeakers must occasionally be disassembled in the field and reassembled and realigned, frequently by inexperienced personnel, this characteristic of the loudspeaker often results in a degradation of performance when, for example, the proper shims are lost or improperly placed.

Another problem associated with the conventional type of construction is that the reaction forces of the radial springs supporting the armature do not act in the same plane as the force acting to move the armature. Consequently, moments are often developed in the bonding area and in the armature itself which are damaging to the bond and cause undue wear between the armature and stator.

In view of the foregoing, it is an object of the present invention to provide an air modulated loudspeaker in which misalignment of the stator and armature is prevented.

It is an additional object of the present invention to provide a loudspeaker construction in which resultant forces acting on the armature act substantially along a common axis thereby eliminating any torsion which can otherwise cause undue wear.

Briefly, in accordance with the present invention a modulator assembly is provided in which the armature is coupled to the stator by a cylindrical spring which permits relative axial movement of the armature. By permanently coupling the armature and stator in this manner, the modulator assembly can initially be precisely assembled so as to prevent any future misalignment.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a sectional view illustrating a preferred embodiment of loudspeaker construction in accordance with the present invention;

FIGURE 2 is an enlarged fragmentary sectional view illustrating the air flow through the concentric slotted stator and armature of the modulator assembly;

FIGURE 3 is a horizontal plan view illustrating the concentric cylinders of the modulator assembly;

FIGURE 4 is a fragmentary sectional view illustrating the details of a cylindrical stator in accordance with the present invention;

FIGURE 5 is a fragmentary sectional view illustrating the details of a cylindrical armature in accordance with the present invention;

FIGURE 6 is a schematic perspective view of a ring illustrated to facilitate an understanding of the spring portion of the armature; and

FIGURE 7 is a schematic perspective illustration of a cylindrical spring of the type employed in the armature of FIGURE 5.

Attention is now called to FIGURE 1 which comprises a sectional view of a loudspeaker 10 constructed in accordance with the teachings of the present invention. The loudspeaker 10 is comprised of a cylindrical casing 12 having a plate 14 secured across the bottom thereof as by welding. The plate 14 defines a central aperture 16. An air intake coupler 18, having a terminal flange 20, is secured to the plate 14 around the aperture 16 by any suitable means. An air filter 24 is secured within the casing 12 in alignment with the aperture 16.

A support web comprised of several individual L-shaped members 26 is mounted on the inner surface of the casing 12. The members 26 define horizontally extending portions 28 on which a permanent magnet assembly 30 is supported.

The magnet assembly 30 includes an upper soft steel piece 31 partitioned into sections 31A, 31B, and 31C. Air gaps 32 are defined between sections 31A and 31B and between sections 31B and 31C. A pair of permanent magnets 36 and 38 contact the sections 31A and 31C respectively. A soft steel piece 40 bridges the magnets 36 and 38. Member 40 rests on the horizontal portions 28 of the L-shaped members 26 and is secured thereto by any suitable means. The section 31B is supported by and spaced from the member 40 by spacers 41.

A modulator assembly 42 is provided and supported in the center of the casing 12. The assembly includes a stator cylinder 44 and an armature cylinder 46. The cylinders 44 and 46 are concentrically oriented and attached adjacent their upper ends as is best shown in FIGURE 2. More particularly, the stator cylinder 44 is provided with an externally projecting peripheral flange 48 adjacent the upper end thereof which is attached to, as by cementing, the inner surface of the armature cylinder 46. In addition, the stator cylinder 44 is provided with an internally projecting peripheral flange 50 adapted to seat on a cutout 52 formed on the upper surface of the magnet section 31B.

The magnet section 31B defines an internally threaded central aperture 54 adapted to threadedly receive a holddown bolt 56. The bolt 56 secures a clamp member 58 to the sectiton 31B thereby locking the flange 50 of the stator 44 therebetween. The bolt 56 is preferably provided with a central passageway 60 to permit voice coil cooling air to exhaust to the atmosphere therethrough.

In accordance with the most significant aspect of the present invention, the armature 46 includes a spring portion 62 (FIGURE to be more specifically described hereinafter. In addition, the armature 46 includes a modulation slot portion 64 defining slots 65 adapted to be aligned with slots 67 in the modulation slot portion 66 of the stator (FIGURE 4). A voice coil 68 wound about the armature 46 is positioned so as to project into the gap 32 between the magnet sections 31A and 31B and between the sections 31B and 31C. The voice coil 68 is electrically connected to conductor 72 which in turn is connected to an electrical connector 74 mounted on the outer surface of the casing 12.

A removable cover plate 90 is secured, as by bolting, to the upper end of the cylindrical casing 12. Supported within an aperture 92 defined in the cover plate 90 is a throat piece 98 secured to the cover plate. The throat piece 98 extends into the stator cylinder 44 and is flared outwardly at its end 104 to engage the inner surface of the stator. An O-ring 106 serves to seal, and thus prevent air flow, between the throat piece 98 and the stator 44. An acoustic horn 108 is mounted on the cover plate 90 in alignment with the throat piece 98.

In the use of the loudspeaker of FIGURE 1, an air compressor (not shown) is coupled to the loudspeaker intake coupler 18 and provides compressed air through the filter 24. Although small amounts of cooling air will pass through passageway 60 for example, the largest volume of air will, as shown in FIGURES l and 2, pass through the modulation slots defined in the armature 46 and the stator 44 into the throat piece 98. As can be seen best from FIGURE 2, the degree of alignment between the modulation slots 65 in the armature 46 and slots 67 in the stator 44 determine the impedance to which the air flow is subjected. Thus, by varying the alignment, the air flow impedance is correspondingly varied to thus in turn vary the acoustic output provided by the loudspeaker 10.

In accordance with the present invention, the alignment is varied by energizing the voice coil 68 which coacts with the magnetic field set up by the permanent magnet sections 31A, 31B, 31C to apply an axial force along the armature 46. As a consequence of this axial force, the spring portion 62 of the armature can very slightly expand or contract, as will be explained in more detail hereinafter, to thus vary the alignment and vary the air flow impedance.

Attention is now called to FIGURES 4 and 5 which respectively illustrate in much greater detail the construction of the armature and stator respectively. The spring portion 62 of the armature 46 is comprised of a plurality of rows of slots 120. Although five rows of slots are illustrated in FIGURE 5, this number is not critical and a greater or lesser number of rows could be employed. The spaced rows of slots in the spring portion 62 effectively define toroidal rings or beams 122 therebetween. The vertical portions 124 defined between adjacent slots in the spring portion 62 effectively act as load columns on the toroidal beam therebeneath and support columns on the toroidal beam above. As a consequence, the toroidal beams can fiex slightly to permit slight axial movement of the modulation slot portion 64 relative to the modulation slot portion 66 of the stator 44.

In order to better understand the functioning of the spring portion 62 of the armature 46, attention is now called to FIGURE 6 which illustrates a single ring 128 of some suitable material supported at two points 180 apart. Also assume that the ring of FIGURE 6 is loaded at two points 90 from each of the support points. It should be apparent that if the ring of FIGURE 6 is of Suitable material, it can flex slightly as the load or support forces are relatively increased or decreased. The ring of FIGURE 6 therefore comprises a simple coaxial spring. For maximum efliciency, a single ring as shown in FIG- URE 6 should not be utilized as the spring portion of the armature inasmuch as it has only two load points and would not satisfactorily distribute reaction forces to all the armature columns, i.e., the columns 130 defined in the modulation slot portion 64. This of course suggests that the spring of FIGURE 6 can be improved by selectmg a greater number of load and support points while maintaining each load point midway between adjacent support points and vice versa. By so increasing the number of load and support points acting on the spring of FIGURE 6, any axial force applied thereto will be well distributed thereby minimizing twisting torque. FIGURE 7 is a schematic perspective representation of a complete spring employing the ring 128A of FIGURE 6 and incorporating first and second mounting rings 132 and 134. The four columns 136 connecting mounting ring 132 to ring 128A can be considered as load columns and the columns 138 connecting ring 128A to mounting ring 134 can be considered as support columns. Thus, it should be appreciated that the construction of FIGURE 7 comprises a coaxial spring which can be compressed and extended by slight amounts while minimizing the tendency to twist the beams. The construction of FIGURE 7 can be extended with the pattern thereof repeated any number of times to achieve any desired set of spring parameters. It Wlll be appreciated that the spring portion 62 of the armature 46 merely comprises an embodiment of the spring representation shown in FIGURE 7. Thus, the spring portion 62 can be considered as having a top mounting ring and a bottom mounting ring 152 with the rings defined therebetween effectively comprising toroidal beams which can be slightly flexed.

It is desirable, as shown in FIGURE 5, that the load columns 154 acting on the bottom mounting ring 152 be aligned with the columns 130 defined in the modulation slot portion 64.

It should be appreciated that the armature 46 and stator 44 can each be produced by conventional precision machining techniques. After manufacture, the stator 44 and armature 46 are secured together by mating the flange 48 of the stator 44 to the inner surface of the armature cylinder 46, as by welding or cementing. Regardless of what securing technique is employed, once the stator 44 and armature 46 are secured together, there is no possibility of misalignment. As a consequence, in order to disassemble the loudspeaker 10, it is merely necessary to remove the cover plate 90 and throat piece 98, prior to unscrewing the hold-down bolt 56. Thereafter, the clamp 58 can be removed and the entire modulator assembly 36 can be lifted from the casing 12. The modulator assembly 42 can thereafter be replaced without requiring that the armature and stator bealigned inasmuch as, as a consequence of securing them" together at their upper edge, they are prevented from ever becoming misaligned. Thus, the loudspeaker can be assembled by inexperienced personnel under field conditions. This represents a considerable advantage over prior art systems in which microscopes are normally required to properly align the armature and stator to achieve maximum loudspeaker efliciency.

From the foregoing, it should be appreciated that an improved air modulated loudspeaker has been disclosed herein which employs a unitary modulator assembly in which misalignment of an armature and a stator is prevented. In addition, wear and maintenance of the modulator assembly are also minimized as a consequence of constructing the armature so that reaction forces act in the direction of armature movement, i.e. axially.

What is claimed is:

1. An air modulated loudspeaker including:

a modulator assembly comprised of first and second concentrically oriented cylinders each having first and second ends; i

a plurality of slots defined in each of said cylinders;

a concentric spring means physically coupling said first cylinder first end to said second cylinder first end;

means fixedly mounting said second cylinder second end in said loudspeaker; and

means for axially moving said first cylinder for varying the alignment between said slots of said first and second cylinders.

2. The loudspeaker of claim '1 wherein said means for moving said first cylinder includes means for applying an axial force thereto.

3. The loudspeaker of claim 2 wherein said means for applying said axial force includes an electrical conductor concentrically wound on said first cylinder.

4. In an air modulated loudspeaker, a modulator assembly comprising:

first and second concentrically oriented hollow cylinders each having first and second ends;

means securing said first ends of said cylinders together;

said first cylinder including a spring portion adjacent the first end thereof and a modulation slot portion remote from the first end thereof;

said second cylinder including a modulation slot portion substantially aligned with said first cylinder modulation slot portion; and

means for applying an axial force to said first cylinder for varying the alignment between said first cylinder modulation slot portion and said second cylinder modulation slot portion.

5. The loudspeaker of claim 4 wherein said spring portion includes at least two spaced rows of slots extending around said cylinder and defining a toroidal beam therebetween having first and second sets of columns respectively extending in opposite directions therefrom.

6. The loudspeaker of claim 5 wherein said columns of each of said sets are uniformly spaced.

7. The loudspeaker of claim 6 wherein each of said columns of said first and second sets is positioned substantially midway between adjacent columns of the other set.

8. The loudspeaker of claim 4 wherein said first cylinder modulation slot portion includes at least one row of slots extending around said cylinder and arranged to define a set of axial columns.

9. The loudspeaker of claim 8 wherein said spring portion includes at least two spaced rows of slots extending around said cylinder and defining a toroidal beam therebetween having first and second sets of columns respectively extending in opposite directions therefrom.

10. The loudspeaker of claim 9 wherein said columns of said second set are aligned with said columns of said set of axial columns.

References Cited UNITED STATES PATENTS 1,149,583 8/1915 Hutchison 340-405 JOHN W. CALDWELL, Primary Examiner. HAROLD I. PITTS, Assistant Examiner.

US. Cl. X.R. 340-405 

